Circuit City Cessna 560 Pueblo, CO February 16, 2005

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Circuit City Cessna 560Pueblo, CO February 16,
2005

Dr. Daniel Bower Aircraft Performance
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Overview

• Types of icing environments- SLD
• Accident aircraft performance
• Cessna 560 modified stall warning system
• De-ice boot activation
• Automatic mode for de-ice boots
• Previous icing recommendations

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Part 25 Appendix CContinuous Maximum
97-99
LWC
SLD
40µ
15µ
MVD
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Effect of SLD on ice accretion
Wing leading edge cross section
Appendix C
Direction of flight
SLD
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Front Edge of Wing
Rough Ice
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Altitude Time History
Gray ice mentioned
De-ice boots operated
Clear ice mentioned
Stall
PUB
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Accident Airplane Relevant Speeds
114
Approach speed in icing
90
Accident Stall Speed
86
Ice Stick Shaker
81
Ice Stall Speed
Clean Stall Speed
76

Knots
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Accident Sequence

• Airplane slowed below Vapproach
• De-ice boots not operated in second icing layer
• Presence of an estimated 1/6 of an inch or less
  of ice accreted in SLD conditions caused the
  airplane to stall prior to stick shaker
• Airplane entered a rapid left roll
• Airplane did not recover in the 1,500 feet agl
  available

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Stall Warning modifications

• 1996 - In response to 3 accidents in icing
  conditions FAA performed flight testing with
  artificial 1/2-inch ice shapes.
• Ice Shape generated using one App C condition
• Larger droplets not considered
• Resulted in modifications to stall warning system
  to increase stick shaker speed in icing
  conditions

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De-ice Boot Operation

• 1998 NTSB issued Rec. A-98-91 to activate deice
  boots upon entering icing conditions
• FAA issued NPRM for several airplanes including
  the 560.
• Cessna used results from 1996 flight tests with
  1/2-inch ice shape to request withdrawal of NPRM
• FAA withdrew NPRM

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De-ice Boot Operation

• Current company and manufacturer guidance states
  boots should be operated when ice is 1/4- to
  1/2-inch thick, and AFM states
• early activation of the boots may result in ice
  bridging on the wing
• Deice Boot Bridging Ice in the shape of an
  inflated deice boot forms as the boot is cycled,
  which cannot be removed by subsequent cycles

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De-Ice Boot Bridging - Recent research

• 1997 Deice Boot Bridging Workshop
• FAA AC 25.1419 (2004)
• Recent research by FAA
• No evidence that modern turbine powered airplanes
  are at risk for bridging
• Total number of accidents investigated by the
  Board related to bridging

0
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Automatic boot cycle

• Bridging is no longer a valid reason to allow a
  buildup between boot cycles
• Research by FAA indicates residual ice is not as
  detrimental as intercycle ice
• Manually operated boots can lead to excessive
  intercycle ice buildup in high workload situations

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Revised Icing Certification

• Upgrade aircraft icing certification criteria to
  include SLD (A-96-54)
• Research into effects of in-flight icing,
  including intercycle and residual ice
  (A-98-92)
• All de-ice boot aircraft certified for icing
  should be subject to revised icing criteria

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Summary

• Airplane slowed below approach speed
• Deice boots were not operated during approach
• Airplane encountered supercooled large droplets
• Caused a thin, rough ice accretion with large
  aerodynamic penalties
• Stall warning was inadequate
• Ice accretions used to determine the stall
  warning margin were not representative of the
  most detrimental

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Summary

• Deice Boots bridging is not a concern
• Warrants activation of deice boots upon entering
  icing conditions
• Warrants development of system for automatically
  cycling of deice boots
• Icing certification standards
• Need to be updated based on accident history and
  recent research, and applied to all deice boot
  equipped aircraft

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